The mobile internet is currently not working at all for me when using SIM slot 2.
Although an IPv4 and an IPv6 address have been assigned, “limited connectivity” is displayed under “Mobile network” and the mobile Internet does not work. See above
I experimented a bit more and found the following workaround for using mobile internet with SIM slot 2:
By switching the network mode to “2G only”, the connection is re-established and “Connected” is now displayed under “Mobile network”.
If you then switch back to the “4G preferred” network mode, the mobile data connection remains “Connected” and the mobile Internet connection works correctly with 4G.
When connecting to a WLAN, the mobile data connection is disconnected as expected. After logging out of the WLAN, the mobile data connection is correctly established again.
So far so good, but unfortunately after restarting the phone or after toggling the flight mode, the previous problem reoccurs and the above process has to be repeated.
And of course VOLTE still doesn’t work with SIM slot 2.
But better than nothing and finally a reproducible behavior.
However, this trick does not help with the actual problem with SIM slot 1 (no IPv4 mobile data connection).